To make informed prevention resource allocation decisions, public health decision makers require detailed informafion about the cost, cost-effecfiveness, and potential impact of various strategies to prevent transmission of HIV and other STDs. The Cost-Effecfiveness Modeling Core supports scientific research into the cost, economic efficiency, and effectiveness of HIV/STD prevention intervenfions, related behavioral modificafion programs, and intervenfion disseminafion and technology transfer activifies. The Core provides consultafion to CAIR Investigators regarding the feasibility of conducting economic efficiency or modeling studies of proposed, ongoing, or completed HIV prevention and disseminafion/technology transfer interventions. Core Scientists idenfify appropriate economic evaluafion or mathemafical modeling techniques for assessing the cost-effectiveness ofthe intervention and collaborate with other CAIR Scienfists on the design of suitable behavioral measurement and cost data collecfion instruments to support economic evaluation research and modeling studies. Core Scienfists take a lead role in performing these analyses. The Core's support activifies include prospective cost data elicitafion during the course of an ongoing intervenfion trial; retrospective data collection after a trial is complete; mathemafical modeling to quantify intervenfion effectiveness in epidemiologically-meaningful units (e.g., HIV infecfions averted or expected number of secondary infecfions); and/or cost-effectiveness, cost-ufility, or other economic analyses to determine the overall economic efficiency of HIV prevenfion interventions.